1. Field of the Invention
The present invention relates to a ceramic structure having a plurality of ceramic sintered bodies connected to each other with connecting members interposed therebetween, a method for manufacturing the ceramic structure, and a nonreciprocal circuit device including the ceramic structure.
2. Description of the Related Art
In recent years, concomitant with the trend toward miniaturization, weight reduction, and reduction in thickness of electronic devices, reduction in height thereof has been required. Accordingly, the reduction in height of electronic devices has been achieved by mounting semiconductor devices or the like in a multilayer structure which is formed of a plurality of ceramic substrates. In this case, the ceramic substrates are connected to each other with electrically conductive bumps provided therebetween.
FIG. 17 is a schematic cross-sectional view showing a related ceramic structure. As shown in FIG. 17, ceramic substrates 901a and 901b are connected to each other via conductive bumps 903 formed on electrode pads 902, the conductive bumps 903 being composed of solder or the like. The electrode pads 902 are connected to conductors 904 located inside of the ceramic substrates 901a and 901b (for example, see Japanese Unexamined Patent Application Publication No. 11-135711 (pp. 4 to 7 and FIG. 4).
The ceramic substrates 901a and 901b are connected to the conductive bumps 903 as described below. First, metal balls are molten and provided on the electrode pads 902, and the ceramic substrate 901b with the metal balls tightly fixed thereto is pressed onto a flat surface of a base substrate, so that balls partly having a flat surface are obtained. The balls partly having a flat surface are brought into contact with a conductive adhesive applied on a support substrate so that the conductive adhesive is transferred onto the balls, and after the balls thus obtained are positioned so as to be brought into contact with a conductive pattern 905 of the ceramic structure 901a, the ceramic substrates 901a and 901b are connected to each other.
However, in the method described above, it is necessary that the ceramic substrates 901a and 901b be formed beforehand and be positioned to be electrically connected to each other. In addition, since the conductive bump 903 is formed by melting a metal ball, it is difficult to control the shape of the metal ball after melting. Furthermore, when the metal ball is connected to the substrate by applying a pressure, displacement of the metal ball may occur in some cases. Hence, it has been difficult to form the conductive bump 903 as it is designed.